The first generation of stars in LCDM cosmology

Abstract

We have performed a large set of high-resolution cosmological simulations using smoothed particle hydrodynamics to study the formation of the first luminous objects in the LCDM cosmology. We follow the collapse of primordial gas clouds in eight early structures and document the scatter in the properties of the first star-forming clouds. Our first objects span formation redshifts from z~10 to z~50 and cover an order of magnitude in halo mas. We find that the physical properties of the central star-forming clouds are very similar in all of the simulated objects despite significant differences in formation redshift and environment. The physical properties of the clouds have little correlation with spin, mass, or assembly history of the host halo. The collapse of protostellar objects at higher redshifts progresses much more rapidly due to the higher densities, which accelerates the formation of molecular hydrogen, enhances initial cooling and shortens the dynamical timescales. The mass of the star-forming clouds cover a broad range, from a few hundred to a few thousand solar masses, and exhibit various morphologies: some of have disk-like structures nearly rotational supported; others form flattened spheroids; still others form bars. All of them develop a single proto-stellar `seed' which does not fragment into multiple objects up to the moment that the central gas becomes optically thick to H2 cooling lines. At this time, the instantaneous mass accretion rate onto the centre varies significantly from object to object, with disk-like structuress have the smallest mass accretion rates. The formation epoch and properties of the star-forming clouds are sensitive to the values of cosmological parameters.